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Voyagers to the Outer Planets
Volume 2 - Uranus
Images 26440.04 to 26949.43 in Compressed Format
This compact read-only optical disk (CD-ROM) is the second of three CD-ROM
volumes containing the images returned by NASA's Voyager 2 spacecraft
during its encounter with the planet Uranus. The next volume in the
"Voyagers to the Outer Planets" series will complete the collection of
images from Uranus. There will be additional volumes in the series
containing images from the other planets visited by the twin Voyager
spacecraft.
This disk contains images taken during the near encounter phase, when
Voyager 2 made its closest approach to Uranus in January 1986. The
disk contains the best images of the rings and the satellites of Uranus.
The images on this disk are the full-resolution (800 pixels by 800 scan
lines) digital images returned by the Voyager cameras. No additional
processing has been performed to enhance the images. The images are
compressed to permit us to pack more data onto each volume but they can
be restored to their original resolution using algorithms described in
documentation on this disk. Image decompression software in several
programming languages is also included on the disk.
As you may have noticed, the file that you are reading now is one of only
two files located in the main directory (the other file, VOLDESC.SFD,
contains general information similar to what you are reading now but in a
format that is easier for computer programs to access). All other files
are located in directories below the main directory. The directory named
DOCUMENT contains a document file named VOLINFO.TXT that describes in
detail the organization of this disk and the format and content of the
Voyager Uranus images. It is highly recommended that you read the VOLINFO
document before trying to process image files.
The directory named INDEX contains a file IMGINDEX.TAB which is an index
to all of the Uranus images. The index table is human and machine readable.
While you can locate images by simply searching through the index yourself,
the table has been designed so that it can be easily loaded into most
database managers for fast and efficient searching. The file named
INDXINFO.TXT in the INDEX directory describes the index table in detail.
The directory named SOFTWARE contains source and executable versions of
image decompression software written in Fortran, C and VAX Macro assembly
language. There is one executable decompression program for IBM PCs and
another for VAX VMS systems. The file named SOFTINFO.TXT in the SOFTWARE
directory describes the software in detail.
Each compressed full-resolution image is contained in a file and the image
files are located in directories named after the principal target of the
image. In alphabetical order the directories containing compressed images
on the Uranus volumes are:
ARIEL - Images of satellite Ariel
MIRANDA - Images of satellite Miranda
OBERON - Images of satellite Oberon
TITANIA - Images of satellite Titania
UMBRIEL - Images of satellite Umbriel
URANUS - Images of Uranus
U_RINGS - Images of the rings of Uranus
In addition there are two catch-all directories containing compressed
images:
CALIB - Calibration images
OTHER - Images that don't fit in any other category
If there are no images of a target on a particular volume then the target's
directory is omitted. If there are more than about 100 images of a target
on a volume, the images are further divided into subdirectories based upon
their image number. Each image subdirectory has a name of the form CnnnnXXX,
where nnnn is the first four digits of the seven-digit image number. All
images of the target with image numbers that have those first four digits
will appear in the subdirectory.
Most files on this disk have a label encoded in the Object Description
Language (ODL). A file's ODL label is readable by both humans and
computers and it provides a formal description of the format and
content of the file. For most files the ODL label appears at the
beginning of the file (this is the case for the file that you are
currently reading). All image files have such an embedded ODL label
preceding the data in the file. For files where labels can't be easily
included, a separate label file is provided that contains the ODL label
and a pointer to the file that the label describes. These external
label files all have a .LBL file extension. An example of an external
label is the file IMGINDEX.LBL in the INDEX directory which contains
the ODL label for the index file IMGINDEX.TAB. The LABEL directory
contains two files with external ODL labels that describe the format
and content of the engineering information that is contained within
each image file. For a description of the Object Description Language,
see the document file VOLINFO.TXT in the DOCUMENT directory.
Please be aware that there are several problems with the first Voyager
Uranus CD-ROM volume. Firstly, 76 images of Uranus were placed into the
wrong subdirectory: these images all have image numbers beginning with
the digits 2624 and hence they should have been placed into a subdirectory
named C2624XXX under the URANUS directory; but due to a juxtaposition of
digits they are instead located in the subdirectory C2264XXX. Secondly the
image file C2625405.IMQ is missing from the disk. Thirdly, the image file
C2449031.IMQ was truncated during processing and the image cannot be
decompressed. We have updated the IMGINDEX.TAB file on this second volume
to point to the actual location of the 76 misplaced files on the first
volume. We have also placed the missing file and the truncated file onto
this volume and updated the IMGINDEX.TAB file to reflect this. We suggest
that you use the index file found on this volume in preference to the index
file on the first volume.